diff --git a/modules/openapi-generator/src/main/resources/php-symfony/ApiPass.mustache b/modules/openapi-generator/src/main/resources/php-symfony/ApiPass.mustache
index 7e6ca5de4011..8404aca50d54 100644
--- a/modules/openapi-generator/src/main/resources/php-symfony/ApiPass.mustache
+++ b/modules/openapi-generator/src/main/resources/php-symfony/ApiPass.mustache
@@ -40,7 +40,7 @@ class {{bundleName}}ApiPass implements CompilerPassInterface
      *
      * @param ContainerBuilder $container
      */
-    public function process(ContainerBuilder $container) {
+    public function process(ContainerBuilder $container) : void {
         // always first check if the primary service is defined
         if (!$container->has('{{bundleAlias}}.api.api_server')) {
             return;